1. Field of the Invention
The fields of art to which the claimed invention pertains are catalytic composites and methods of manufacturing catalytic composites. More specifically, the claimed invention relates to the method of manufacture of a zeolitic catalytic composite, and a method of calcining zeolitic catalysts at relatively low temperatures.
2. Description of the Prior Art
Crystalline aluminosilicates, or zeolites, are well-known in the art and have found extensive application as hydrocarbon conversion catalysts or as a component thereof. Such materials are of ordered crystalline structure often visualized as a three-dimensional network of fundamental structural units consisting of silicon-centered SiO.sub.4 tetrahedra and aluminum-centered AlO.sub.4 tetrahedra, the tetrahedra being interconnected by a mutual sharing of apical oxygen atoms and arranged to form cages or cavities in open communication through smaller intracrystalline channels of pore openings whose narrowest cross section has essentially a uniform diameter characteristic of each crystalline aluminosilicate variety. To effect a chemical balance, each AlO.sub.4 tetrahedra has a cation associated therewith--usually a sodium or other exchangeable cation. The aforementioned cages or cavities are occupied by water molecules and by the cations associated with the tetrahedra, both of which exhibit considerable freedom of movement permitting ion-exchange and reversible dehydration.
Zeolites are typically used as catalysts alone or composited with other materials. The other materials may serve as catalytic agents or, more commonly, as relatively inert supports for the zeolites. Amorphous silica-alumina is frequently composited with zeolite to form hydrocarbon conversion catalysts.
Most uses of zeolitic catalysts in hydrocarbon conversion reactions require that prior to use the catalyst be calcined at a relatively high temperature to activate and partially dehydrate the catalyst. Temperatures in the range of from about 1500.degree. F. to about 1700.degree. F. are commonly used. However, high temperature calcination of zeolitic catalysts reduces the physical integrity of the catalyst, producing a lower yield of finished catalyst. In addition, and at least as important, the susceptibility of the calcined catalyst to attrition during use is increased by high temperature calcination. The latter consideration is particularly important in marine bed applications, such as fluid catalytic cracking processes, in which catalyst life is a function of the catalyst's resistance to attrition.
Heretofore, the competing considerations of catalyst activity and structural integrity had to be carefully balanced during the manufacture of the catalyst. In addition, even high temperature calcination has yielded zeolitic catalysts of lower activity and selectivity than desired.